Suture anchors are used to secure sutures within openings formed in bones during joint reconstructive surgery and arthroscopic surgical procedures. The anchor is typically placed in a bone and connected to a suture that could otherwise not be secured to dense osseous material. Such suture anchors are used, for example, to anchor ligaments or tendons to bones in knee, shoulder and elbow reconstruction and repair operations. Important attributes of bone anchors are that they be easy to insert, and provide a firm anchor. Unintended dislodgement of the anchor after surgery can have serious adverse consequences, hence much importance is placed on the ability of an anchor to resist extraction or withdrawal forces exerted by the attached suture. Such bone anchors may be bioabsorbable or non-bioabsorbable, depending on the type of operation and preference of the surgeon.
An early type of bone anchor took the form of a barb shaped like a fish hook that was inserted into a borehole and hooked into the soft marrow of the bone. A later approach to suture anchors is disclosed in U.S. Pat. No. 4,738,255, which discloses a suture anchor delivery tool that manipulates a specialized two-piece anchor system. The anchor includes a collar with a slotted distal end that expands when a ram member is pulled into the distal end of the collar. The ram is pulled into the slotted collar by tension exerted on a line that runs axially through a mandrel from which the collar is suspended. This complex arrangement requires a specialized anchor delivery system for manipulating the ram and slotted ring. The expanded bone anchor it produced also tapers proximally such that extraction forces exerted on the anchor tend to collapse the enlarged distal portion of the anchor.
U.S. Pat. No. 4,013,071 discloses an orthopedic screw having an expandable tip that enhances bone retention. The expandable tip includes side slits that extend through the distal end of the screw. The side slits produce a distal screw tip that is flared by axially advancing a rod-shaped expansion member through an internal bore of the orthopedic screw. The distal expansion of the screw persists only as long as the rod shaped expansion member is present. Once the expansion member is withdrawn, the tip returns to its original collapsed shape.
Yet another implantable bone anchor is shown in U.S. Pat. No. 4,409,974 wherein a frustoconical anchor body is retained in a bore hole by a plurality of arms that pivot radially outwardly in the bore. The arms are expanded by exerting tension on a series of threads that run axially through an insertion tube. U.S. Pat. No. 4,454,875 discloses an osteal staple having barbed legs with a triangular cross-section that resist withdrawal of the staple from bone.
The bone anchors shown in these prior patents require multiple parts that increase surgical risk and expense. Multiplication of parts increases the possibility that one of the parts will be dislodged or dropped during surgical placement, or lost internally in a patient. These prior anchor systems are also complex and time-consuming to use, requiring assembly and manipulation of multiple parts. Such time-consuming assembly of devices can be expensive to use because of the high cost of time in surgical suites Finally, many of these prior expandable bone anchors can be collapsed by the tension exerted on them by the sutures they anchor.
It is accordingly a primary object of the present invention to provide an improved bone anchor that is inexpensive to manufacture and simple to install
Another object of the invention is to provide an improved bone anchor that does not require time-consuming and expensive assembly of multiple parts, or complex remote manipulation to expand the anchor
Yet another object of the invention is to provide an improved bone anchor having a minimal number of parts that reduces the likelihood of inadvertent loss of anchor pieces during placement.
Yet another object of the invention is to provide an improved bone anchor that better resists extraction forces exerted by suture tension.
Still another aspect of the present invention is to provide an improved bone anchor that is compact and self-seating.
Another important object of the invention is to provide an improved bone anchor that may be formed by a simple molding operation with no close tolerance assembly operations required.
These and other objects of the invention will be understood more clearly by reference to the following detailed description and drawings.